So I also wanted to make my own boombat, but I couldn't find an apt "batten" (that is to say: I couldn't find it quick enough and I was impatient); and I didn't really like the fact that I had to make a small hole in the hem of the sail, although that is quite harmless. Maybe I like booms (for a mainsail) since I am used to it in sailing. Anyhow, I thought it could work, so I made a boom instead.

I wanted the boom to be lightweight (otherwise it will hammer the head rather unpleasantly or even dangerously in a unexpected gybe). Also it should still be possible to have a relatively flat shape of the sail when close hauled, and a more rounded shape for a broad reach or running.

Luckily, all these objectives were easy to achieve.
I took two pvc tubes, one 5/8 inch and one 3/4 inch. These fit in each other.

To stiffen it, I did a bamboo inside. I made the length of the boom a bit longer than the foot of the sail to be able to experiment with the trim. This makes for still rather flexible boom, but for the application it is strong and stiff enough, cheap and very lightweight.
I drilled holes in the ends. With a small rope I have it permanently attached to the sail at the mast-side of the sail. With a rvs karabiner it can be attached to the sheet eye (I hope that is the right term). I can experiment with the trim by adapting the length of the white line (see pic)

The sheet is directly connected to the sail, exactly as is the case without a boom. So the boom is attached to the sail as an extra. The effect is that the sail is sheeted as normal when close hauled. Only when "going broader than a reach" the boom starts acting. This setup works better than with the sheet connected to the boom and the boom to the sail. For then the sail would be too loose close hauled or too flat on a broad reach and the forces on the boom would be bigger, so it should be made stronger (means heavier).

This is how it looks like on my oasis:

By releasing the karabiner and pointing the boom upward along the mast, the sail can easily be furled around it. Furling the sail is even easyer than it was, since I have more grip now.

I find it very convenient that I always have it with me when I have the sail (nothing to forget or loose). Although it is a minor advantage, I like the fact that I can grab the boom easily to gybe in a controlled way. Also: the shape of the sail is not really dependent on the strength of the wind. However, the boom doesn't change the fact that the rear deck of the oasis is a bit short, so that the sheet is angled down a bit too much. But still I'm quite satisfied with the shape of my sail now (also because of the stays).

From the reports here I'm sure the boombat works also very well and it has quite a few other great advantages (even simpler, lighter, stops noisy sail-flapping even better). But I've come to believe that a boom can be a good alternative. In the right winds, my oasis really likes to run now, so I guess I'll stick to it!

This is a the best boom I have ever seen plus, its simple, inexpensive yet efficient design should make it even more appealing to all Hobie Kayak Sailors.

I especially like the "outhaul" white rope option at the end of the boom to trim the sail in various wind conditions.

Do you have a photo of the attachment of your boom to the mast end?
Would it also be possible to use a carabiner clip system on both ends of the boom for quick rigging and detachment ?
The boom could then be strapped to the hull or stowed and used only when needed. etc.

I can envision your boom being adapted to the AI and all other Hobie kayaks with great results.

Thanks guys!
Kep, Below a pic of the mast attachment. (not so clear but I don't have a better one now.) With the yellow rope the boom is attached to the sail (through the eye of the bungee / sail downhaul). I had a piece of plastic (the black thing there) that could be used to have the boom lean against the mast. But it is not necessary. (In fact it is hardly used now because I attached the yellow line too close to the front end of the boom.)
Don't mind the white rope (that's the halyard for the jib).

It is surely possible to use a karabiner clip at the mast side also. But since the bungy already fills the eye, you should put a small line through the eye and clip it on the line. Personally, I like it that it is fixed to the sail, since I always sail with boom (it is automatically kept with the sail, cannot fall out when stored etc).

This boom can be used on all kayaks with the small sail, but I am not so sure that it will be great for the AI. It than has to be much stronger / heavier because the AI sail is much bigger. And because of the sail shape of the AI, the boom will be low and thus can seriously hinder the AI sailer and could even flip him overboard in a gybe.

Hi Ya Scooby
Thanks for your post of the photo of the mast end section of the Scooby boom.
I believe the AI would be unable to furl the main if a boom was firmly attached.

However one great benefit of your Scooby Boom system is that with a carabiner on each end , the boom could be unclipped on one end in a hurry if not both.

If the boom was clipped on to the mast end perhaps the AI sailor could quickly unclip the boom in order to furl the sail.

Then if there was a telescoping version of your boom made with holes and pins to lock any size adjustment in place , the furled sail could be re-fitted to the adjustable Scooby Boom and then clipped back on again for immediate use.

As for the Scooby boom head clearence , I do not know the AI cockpit and control system well enough to determine if the Scooby boom would have room to zoom.

Im sure someone will come along and try your Scooby Boom on an AI someday and then we will know that it works.
I believe it would work quite well and add much improvment to the AI sailing abilities.

G'Day Skua and Kep,
Have you seen this tube clip fitting you can get at camping stores?
It might work well for securing the boom to the mast. It is designed for a 22mm (7/8" ) tent pole which is the same size as the mast.

Looks as if that fitting would be a great way to fit the boom to the mast! A line through the sheet eye is probably still needed, since the boom is not at a right angle to the mast.

I made a pic more close by of the so called "scooby boom system" (I like that name Kep!)

The black plastic fitting-like thing actually was a part of the packing material of a barbie doll or something like that of one of the kids, but, although not essential, it is nice to the job.
I still have to reroute the yellow line, so that the black fitting stays to the mast even when an close hauled.

G'Day Skua,
That's a clearer pic of your boom connection. I like your resourcefulness! The standard Hobie mast coming from the imperial US is 7/8"OD which measures 22.225 mm. Sadly this is not a standard metric tube size. Here in OZ our standard sizes are 20mm, then 25mm with nothing available inbetween. I wonder if your mast is not the genuine Hobie imperial tube but has been substituted for the metric size in Europe? Is it a loose fit in the mast tube?

About my mast:
My sail set came with the normal 22mm standard mast, but wanted something stiffer. I bought two standard alu tubes, 20mm and 25 mm with the plan to put them in each other with only the 20 mm in the mast step. That gives a really nice and stiff mast. But I found out that it was too stiff. Even small movements on the top of the mast directly were translated to movement of the mast button on the bottom of the boat. So I decided it was not wise to go that route and now normally use the 20mm mast. it is a bit more flexible in the lower part, but less flexible in the upper. Overall, I think it helps shape the sail a bit better than the standard mast. But the difference is not that great. The stays are far more important.

What I like is that if anything goes wrong with the stays and the jib out, I think I will break or bent this mast before my mast step will fail. I think that is a good thing...

I managed to put a 22mm plastic plug in the bottom, so only at the top of the mast step the fit is more loose. But since I always use the stays, that is not so important.

It works ok this way. But it would be even better, if I could make the mast step stronger so it could support this stiff (double) mast...